Alzheimer disease (AD) is characterised by a progressive dementia occurring in mid or late life. The first events leading to AD are believed to occur some 10 to 20 years before the cognitive symptoms appear, and evidence suggests that a key event in the pathology of AD is the deposit of extracellular aggregated amyloid β (Aβ) plaques in the brain. Aβ is generated by proteolytic cleavage from the amyloid precursor protein (APP) which is a large transmembrane protein with a suggested neutrophic function. The main Aβ variants observed in the human brain are Aβ 1-40 and Aβ 1-42, but also truncated N-terminal variants and other modified species thereof are observed in the plaques.
Immunotherapy against the Aβ plaques has been shown to disrupt the Aβ aggregates and promote the clearance of plaques in the brain. Both active immunogenic approaches with Aβ or fragments thereof as well as passive immunisation using anti-Aβ antibodies have proven effective in different animal models. Vaccination of humans with Aβ was shown to prevent the development of Aβ plaques and reduce the Aβ burden in patients in a clinical study, however the study was stopped due to inflammation in the brain of some of the patients. An immunogenic strategy to reduce the amyloid plaques thus relies on a delicate balance of activating the immune system but still avoiding an uncontrollable inflammation to occur (Monsonego et al (2003) J clin invest 112, 415-422). This requires a precise knowledge of the chemical nature of inter alia the nature of the deposit. In an attempt to understand the exact composition of the amyloid plaques one of the most abundant N-truncated Aβ peptides identified are carrying a pyroglutamate at position 3 (AβpE3, N-terminally truncated Aβ starting with pyroglutamate) (Saido et al. (1996) Neuron 14, 457-466). These pyroglutamated peptides have been shown to accumulate in plaques as well as around the blood vessels in AD, and due to its hydrophobic potential it has been shown that these peptides increase the aggregation. A recent transgenic mouse model expressing AβpE3-42 in neurons demonstrates that this peptide is neurotoxic in vivo and leads to loss of neurons (Wirths et al. (2009) Acta Neuropathol 118, 487-496).
Antibodies with specificities against the N-terminal pyroglutamate are believed to be advantageous because of their specificity towards only the pathogenic pyroglutamate N-terminal species of Aβ, thereby leaving APP or other cross reacting species untouched. It is thus envisaged that the risk of uncontrollable cerebral inflammation will be reduced compared to antibodies directed to non-pyroglutamated Aβ or fragments thereof.
Antibodies targeting AβpE3 peptides and aggregates have been made (Acero et al (2009) J Neuroimmunol 213, 39-46; Saido et al. (1996) Neuron 14, 457-466; and U.S. Pat. No. 7,122,374) and identification of various AβpE fragments have been hypothesized as epitopes (WO2004/013172; WO2010/009987; WO2010/129276; and Wirths et al. (2010) J Biol Chem 285(53), 41517-24, Epub 2010 Oct. 22).
The present invention provides two highly specific monoclonal antibodies directed against human AβpE3 (5C9 and 2E83, respectively) as well as two highly specific monoclonal antibodies directed against murine AβpE3 (2E4 and 1G11, respectively).